The present invention relates to a device for data transmission in a motor vehicle and/or from a motor vehicle in its vicinity, including a first transceiver unit in or on the motor vehicle and a second transceiver unit which is provided in at least one transponder unit whose spatial position relative to the vehicle may be variable or any desired position.
Such a device is discussed in IEEE Transactions on Industrial Electronics, Vol. 35, No. 2, May 1988 under the title xe2x80x9cKeyless entry system with radio card transponder.xe2x80x9d This data transmission device transmits a coded query sequence via an induction loop mounted on the vehicle, e.g., in an exterior mirror or in the bumper, to a transponder accommodated in a card the size of a credit card, which then delivers a response sequence via an antenna. The transmission frequencies used here are in the range of a few hundred kHz.
In general, the mechanical keys customary in the past are currently increasingly being replaced by electronic systems such as remote control systems using infrared or wireless signals for access authorization to vehicles. In other words, electronically encoded keys are being used to an increasing extent for startup authorization.
Communication systems between vehicles and an infrastructure installation, e.g., for acquisition of road use fees, are also referred to in other prior systems.
Also referred to in other prior systems are radar distance measuring systems which are installed in the vehicle and operate in the gigahertz range and a radar sensor on at least one side of the vehicle for measuring the distance and velocity between the vehicle and an obstacle, e.g., a vehicle driving in front or a parked vehicle.
It is an object of the present invention to utilize in a simple manner a radar transmission channel, which is present in the vehicle for distance measurement, for other data transmission functions which are activated only in conjunction with a data exchange which is deemed valid. Firstly, this should reduce costs in manufacturing these systems in comparison with previous separate radar and data transmission systems, and secondly, the security of the transmission between the vehicle and one or more transponders should increase.
Therefore, in order to achieve the object formulated above, a wireless connection is established between the vehicle and at least one transponder. A particular simplification combined with a simultaneous increase in security is achieved due to the fact that each transceiver unit includes a two-channel data transmission unit whose microwave frequencies for two-channel communication are selected so that their difference yields an intermediate frequency which is processable by using conventional components in a heterodyne receiver of the receiving part of the first and second transceiver.
The orientation of the transmitting and receiving antennas relative to one another is problematical because the spatial position of the transponder, in particular, the key (i.e. key fob) to the vehicle is variable as desired. For example, the key may be in the driver""s pants pocket.
If a linearly polarized antenna is used in the vehicle sensor and a circularly polarized antenna is used in the transponder to achieve this goal, this avoids the case of two linearly polarized antennas which would produce a theoretically infinitely high attenuation of the transmitted signal if their polarization directions were at right angles.
Furthermore, one or more antennas having the most spherical, i.e., omnidirectional characteristic should be used in the transponder (key).
The radar sensor of the vehicle used for measuring distance and velocity is expanded by adding a two-channel data transmission system which may be used for local communication with a key for xe2x80x9ckeyless entryxe2x80x9d applications and also for communication with an installation for acquisition of fees, for telematic applications or other remote control applications.
The two transceivers are configured so that their oscillator signal (LO signal) is used for downmixing in the case of reception. The transmission frequency and the receiving frequency are such that the band limits of the frequency band used may be upheld due to the their frequency shift. Therefore, frequency stabilization need be used on only one side, i.e., on the motor vehicle side or on the transponder side. Therefore, and due to the fact that conventional components may be used, the entire data transmission system may be implemented inexpensively.
The exemplary data transmission device according to the present invention is explained in greater detail below on the basis of the enclosed drawing using exemplary embodiments.